Radiative boilers typically are constructed with pressurized water tubes surrounding a vertically contained heat source. The heat is furnished and controlled by introducing and burning oil or natural gas at many selected points in the vertical structure. Coal-fired boilers operate similarly. The radiation impinges on the water tubes, and the water is heated and transformed first to steam and then to superheated steam which is passed through turbines to generate electrical power.
A major cause of power outages is failure of the pressurized water tubes. A common cause of such failures is stress rupture caused by short-term overheating, high-temperature creep, dissimilar metal welds and/or abrupt or uneven changes of boiler tube temperatures at elevated temperature ranges.
Water tube failures require the unscheduled shutdown of the boiler, sometimes for extended periods. Being able to anticipate water tube time of failure would enable unscheduled shutdowns to be avoided, and enable instead an optimally planned overhaul for the watertubes at the end of their useful lives but before failure.
Unfortunately, the ability to predict tube life in terms, for example, of mean time to failure has been almost wholly lacking in power plant maintenance because of the complex failure mechanisms at work. The one most reliable predictor is considered to be water tube surface temperatures determined over time. Yet, current mechanisms for making accurate water tube surface temperature measures during operation are either prohibitively expensive or short-lived themselves because of the extreme temperatures and corrosive character of the combustion products.